It is well known to provide a motor vehicle with a cooling system in which a pump circulates coolant through the engine, through a radiator to cool the coolant and through a cabin heater which can use the coolant warmed by the engine to provide heating for the vehicle. It is also known to use the coolant to cool one or more auxiliary heat exchangers such as an engine oil cooler.
It is a problem with such known arrangements that when the engine and the vehicle are both cold some of the heat generated by the engine on start-up is absorbed by the auxiliary heat exchangers. Not only does the engine not warm up as quickly as it might but also the supply of heat to the heater is diminished because of the relatively slow warm up.